xu TABLE OF NOTATIONS Ib. = pound, the unit of weight. gm. = gram, pd. = mass of a body which kg. = kilogram. weighs one pound. mm. = millimeter, in. = inch. cm. = centimeter, ft. = foot. . m. = meter. H.P. = horse power. km. = kilometer. S.H.M. = simple harmonic motion. Letters in gothic type denote vector magnitudes. A dot on a letter indicates that the latter is differentiated with respect to time. A letter with a bar above it denotes an average magnitude. The letter " i" when used as a subscript denotes " any one of ... ,"' thus "Fi" stands for "any one of Fit F^ Fs, etc,"